Technical Details for Pulsar VLBI

As discussed before, we have completed multiple pilot projects which provide the technical background for this proposal. Though the scope of this project is substantial, the technical aspects are now routine in nature.

We propose to use three distinct calibration modes for our targets:
  1. If the pulsar flux density is > 30 mJy, we will use the wideband ionospheric calibration approach, phase referencing the observations to a calibrator < 3 degrees away. For these pulsars, preliminary observations are required only in cases where the positions and proper motions are not known with enough accuracy for VLBI. In such cases, a brief preliminary VLA observation (A array, at 1.4 GHz, ongoing) is required. For most of the targets, no preliminary observations are needed.

  2. If the pulsar is not strong enough for wideband ionospheric calibration, we will use in-beam calibration. This requires preliminary VLA imaging to identify possible in-beam calibrators (using A-array, 1.4 GHz data, obtained from archives and ongoing), with follow-up observations at the VLA (A-array, 8.4 GHz) and the VLBA (1.4 GHz) to confirm compactness and suitability. Our past experience suggests that about 1/3 of the investigated pulsars will be found to have suitable in-beam sources within the 30 arcmin primary beam of the VLBA telescopes at 1.4 GHz.

    For cases where the pulsar is modestly strong (flux density > 10 mJy), the in-beam source can be as weak as 2 mJy, since we can self-calibrate the pulsar and perform relative astrometry on the in-beam source. For weaker targets, an in-beam source stronger than about 8-10 mJy will be required to obtain differential phases and delays with respect to the nodding calibrator.

  3. Some targets are not strong enough for wideband ionospheric calibration and might not have suitable in-beam calibrators, but will be observable at 5 GHz with the VLBA. Depending on the calibrator throw, we will optionally use GPS ionospheric calibrations for these phase-referenced observations as well.

Scientific Case
Results from Ongoing Projects
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Shami Chatterjee
Contact Information
Last modified: 14 Feb 2002
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